JPH0545221A - Infrared ray detecting circuit - Google Patents

Abstract

PURPOSE:To prevent change of sensitivity to be caused by ambient temperature, and detect information of the ambient temperature and radiation heat individually by providing a reference heat sensitive resistor for sensing change of the ambient temperature in addition to an infrared sensitive resistor. CONSTITUTION:Besides an infrared sensitive resistor Rt for sensing radiation energy of the infrared ray and ambient temperature, a reference heat sensitive resistor Rref having nearly the same temperature-resistance characteristic and for sensing change of the ambient temperature is provided. Since resistance value of the resistor Rref is decided on the basis of only the ambient temperature, only the information on the ambient temperature can be taken out on the basis of an equation wherein output voltage 3 of a direct circuit amplifier 2=2X Vref. Differential amplification of the voltage V3 and input voltage Vin is performed by a direct current differential amplifier 3 to take out only the information on radiation heat as output voltage V2. Furthermore, input voltage Vin is amplified by an alternating current amplifier 1 as output voltage V1 to detect change quantity of radiation energy. Change quantity of radiation energy input to the resistor Rt, an absolute value of radiation energy, and the ambient temperature can be detected in-dependently on the basis of these output voltage V1, V2, V3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared detecting circuit, for example, detecting infrared energy radiated from a human body to detect the movement or presence of the human body, or detecting indoor radiant energy or room temperature. It is used to control the air conditioning.

[0002]

2. Description of the Related Art FIG. 3 shows a conventional infrared detecting circuit. In the figure, Rt is an infrared sensitive resistor. This is composed of a resistor (for example, a thermistor) that changes its resistance value due to a temperature change. Rin is an input resistance. This is a resistor for converting a change in resistance value of the infrared sensitive resistor Rt into a change in voltage. E is a direct current power supply, which divides the direct current voltage by the infrared sensitive resistor Rt and the input resistance Rin to convert the change in resistance value of the infrared sensitive resistor Rt into a change in input voltage Vin. The input voltage Vin is input to the AC amplifier 1 and the DC amplifier 2, and the AC component and the DC component are amplified respectively. When the above signal processing is expressed by an equation, Vin = E × Rin / (Rin
+ Rt).

FIG. 4 shows a typical resistance value-temperature characteristic of the infrared sensitive resistor Rt. In the figure, the vertical axis represents the resistance value (Ω) of the resistor Rt, which is expressed in logarithm. The horizontal axis represents the temperature (° C.) of the resistor Rt. By making the heat capacity of the resistor Rt as small as possible and making the heat resistance as large as possible, the temperature of the resistor itself can be raised and the resistance value can be changed even with a slight radiation heat (infrared ray).

FIG. 5 shows the configuration when this infrared detecting circuit is applied to the movement detection of a human body. In the figure, L is an optical system, which is composed of, for example, a convex lens or a concave mirror. F is a detection field of view, and has a size in which the resistor Rt is projected through the optical system L. When an infrared radiator (for example, a human M) enters the detection visual field F, the infrared ray is received by the resistor Rt via the optical system L, and the temperature of the resistor Rt rises due to the radiant heat of the infrared ray. And the resistor Rt
By amplifying the input voltage Vin obtained by dividing the voltage of the DC power source E by the input resistance Rin and the AC amplifier 1, it becomes possible to detect the movement of the human body as the change of the input voltage Vin.

Here, the waveform of each part when an infrared radiator (for example, a human M) moves across the detection field of view F is shown in FIG.
Shown in. In the figure, (a) is a change in the radiant energy in the visual field when a human M having infrared radiant energy passes through the detected visual field F. (B) is a change in resistance value caused in the infrared sensitive resistor Rt by the radiant heat from the human M. (C) is an infrared sensitive resistor Rt
This is a change in the input voltage Vin to the AC amplifier 1 due to a change in the resistance value caused by. (D) is the input voltage V
This is a change in the output voltage V1 when the change in is amplified by AC.

As described above, when the infrared detection circuit is applied to the movement detection of the human body, the resistance value of the infrared sensitive resistor Rt changes when the human M having the infrared radiation energy passes through the detection visual field F. It is possible to detect the movement of the human M by AC-amplifying the change in the resistance value as the change in the voltage value.

[0007]

In the conventional infrared detecting circuit as described above, the resistance value of the infrared sensitive resistor Rt greatly changes depending on the ambient temperature, so that the sensitivity changes depending on the temperature. .. That is, the change dVin of the detected input voltage Vin with respect to the minute displacement dRt of the infrared sensitive resistor Rt is Vin = E × Rin / (Rin + Rt), and thus dVin / dRt = −E × Rin / (Rin + Rt) −E × Rin × dRt / (Rin + R
t) In the above equation, Rt = 100 to 10KΩ, Rin = 1K
Ω, E = 10V, and dRt (%) = 1%. However,
dRt (%) is defined by% of change with respect to the resistance value at each temperature. Therefore, the amount of change in resistance value (Ω) changes at each temperature.

FIG. 7 shows the result of calculating dVin under the above conditions. In the figure, Rt is divided by Rin to normalize the horizontal axis. As is clear from the figure, d
Vin shows the maximum value at Rt = Rin, and Rt ≠ R
It can be seen that the sensitivity is lowered in the in.

Further, in the above-mentioned conventional example, the detected input voltage Vin contains information on ambient temperature and radiant heat, and it is difficult to extract information on only radiant heat or ambient temperature. This is because the detection voltage Vin changes depending on both the amount of radiant heat and the ambient temperature. However, as shown in FIG. 5, if the detected input voltage Vin is AC-amplified, the ambient temperature change is generally very slow, so that it does not appear in the output voltage V1 of the AC amplifier 1 and only the information due to radiant heat is output. You can take it out. Usually, the movement of the human body is detected by detecting the change in the radiant heat information. However, it is difficult to extract only the direct current information of the radiant heat due to the above reason, which makes it difficult to detect the presence of the human body.

The present invention has been made in view of the above points, and an object of the present invention is to provide an infrared detection circuit capable of preventing the sensitivity from changing due to the ambient temperature. Another object of the present invention is to provide an infrared detection circuit capable of individually detecting information on ambient temperature and radiant heat.

[0011]

In order to solve the above-mentioned problems, an infrared detecting circuit according to a first aspect of the present invention has a structure shown in FIG.
As shown in FIG. 5, an infrared sensitive resistor Rt sensitive to infrared radiant energy and ambient temperature, and a reference thermal resistor Rref sensitive to a change in ambient temperature with substantially the same temperature-resistance characteristics as the infrared sensitive resistor Rt. A direct current source Is for flowing a current through a series circuit of the infrared sensitive resistor Rt and the reference thermal resistor Rref; an AC amplifier 1 for AC amplifying a first voltage Vin obtained in the series circuit; Second voltage Vref obtained at the reference thermal resistor Rref
Is provided, and a DC differential amplifier 3 that amplifies a difference between the output voltage V3 = 2 × Vref of the DC amplifier 2 and the first voltage Vin is provided. ..

Further, in order to solve the same problem, in the infrared detecting circuit according to the second aspect, as shown in FIG. 2, an infrared sensitive resistor Rt sensitive to the radiant energy of infrared rays and the ambient temperature, In order to pass a current through a reference thermosensitive resistor Rref that has a temperature-resistance characteristic substantially the same as that of the infrared sensitive resistor Rt and is sensitive to changes in ambient temperature, and a series circuit of the infrared sensitive resistor Rt and the reference thermosensitive resistor Rref. Voltage-controlled DC current source If, an AC amplifier 1 for AC-amplifying the first voltage Vin obtained in the series circuit, and a second voltage Viv obtained in the reference thermosensitive resistor Rref.
And a reference voltage Vref, a first DC differential amplifier 4, an integrator 5 that integrates the output voltage of the first DC differential amplifier 4, and a second voltage Viv that is the reference voltage Vref.
A feedback circuit that feeds back the output voltage V4 of the integrator 5 as a control voltage of the voltage-controlled DC current source If so as to be equal to the difference between the voltage twice the reference voltage Vref and the first voltage Vin. And a second DC differential amplifier 3 for amplifying

[0013]

According to the invention of claim 1 or 2, an infrared sensitive resistor Rt sensitive to infrared radiation energy and ambient temperature.
In addition, the reference thermosensitive resistor Rr which has substantially the same temperature-resistance characteristic as the infrared sensitive resistor Rt and is sensitive to changes in ambient temperature.
ef is provided to supply a current from the direct current source Is or If to the series circuit of the resistors Rt and Rref, and the input voltage Vin obtained in the series circuit of the resistors Rt and Rref.
And the difference between the predetermined reference voltage 2 × Vref and the DC differential amplifier 3 are amplified, the influence of ambient temperature can be removed and the absolute value of the radiant heat can be detected independently. Even if the temperature changes, the infrared detection sensitivity can always be maximized. The ambient temperature information can be detected as the voltage V3 or V4 by detecting the change in the resistance value of the resistor Rref due to the radiant heat.

[0014]

1 is a circuit diagram showing the configuration of the invention described in claim 1. In FIG. In FIG. 1, Rt is an infrared sensitive resistor, which is a resistor that changes its resistance value with temperature change. By making the heat capacity of the resistor as small as possible and making the heat resistance as large as possible, the temperature of the resistor itself can be raised and the resistance value can be changed even with a slight radiation heat (infrared ray). Next, Rref is a reference thermal resistor. This is a resistor having exactly the same resistance value and resistance change rate as the infrared sensitive resistor Rt. However, it is completely shielded from radiant heat from the outside. That is, the radiant heat due to infrared rays is blocked by a method that does not affect the resistance value or the rate of resistance change, or a method that is spatially insulated. Therefore, each of the resistors Rt and Rref with respect to the change of the ambient temperature.
Has the same resistance value and changes, and when radiant energy due to infrared rays enters, the resistance value changes only for the resistor Rt.

Is is a direct current source, and each resistor Rt,
A constant direct current for converting the change in resistance value of Rref into a voltage is supplied. The DC current source Is converts the current flowing through the resistors Rt and Rref into the input voltage Vin. The input voltage Vin is a voltage obtained by converting the resistance value change of (Rt + Rref), and Vin = (Rt + Rr
ef) × Is, which is the input voltage to the AC amplifier 1 and the DC differential amplifier 2. Further, the current flowing through the resistor Rref by the direct current source Is is equal to the reference voltage Vref.
Is converted to. This reference voltage Vref is Vref = R
It is given by ref × Is, is DC-amplified twice by the DC amplifier 2, and is output as an output voltage V3 = 2 × Vref. Further, this output voltage V3 is applied to the DC differential amplifier 3
It becomes the reference input of. To the other input of the DC differential amplifier 3, the input voltage Vin in which the resistance value changes of the resistors Rt and Rref are converted is applied. The input voltage Vin is AC-amplified by the AC amplifier 1 to obtain the output voltage V1.
Further, in the DC differential amplifier 3, the input voltage Vin and 2 × V
The difference in ref is DC-amplified to obtain the output voltage V2.

The operation of the circuit shown in FIG. 1 will be described below. In FIG. 1, the reference voltage Vref is Vref =
It is given by Rref × Is, but the reference thermal resistor Rre
Since the resistance value of f is determined only by the ambient temperature,
As the output voltage V3 = 2 × Vref, only the information on the ambient temperature can be taken out. In addition, the reference voltage Vref
Voltage doubled by DC amplifier 2 V3 = 2 × V
By performing the differential amplification of ref and the input voltage Vin by the DC differential amplifier 3, only the radiation heat information can be extracted as the output voltage V2. This is because when there is no radiant energy from the outside, Rt = Rref and Vin = (R
t + Rref) × Is = 2 × Rref × Is = 2 × Vr
This is because ef holds and V2 = Vin− (2 × Vref) = 0. Therefore, even if the ambient temperature changes, the output voltage V2 constantly maintains 0 V, and the output voltage V2 appears only when the resistance value of the resistor Rt changes due to radiant heat.

Further, as the output voltage V1, as in the conventional example, the input voltage Vin is AC-amplified by the AC amplifier 1, so that the change in the radiant energy can be detected. The above three output voltages V1, V2
By using V3, it is possible to independently detect the change amount of the radiant energy incident on the infrared sensitive resistor Rt, the absolute value of the radiant energy, and the ambient temperature.

FIG. 2 is a circuit diagram showing a configuration of the invention described in claim 2. In FIG. 2, Rt is an infrared sensitive resistor,
Rref is a reference thermosensitive resistor, and these are similar to the resistors Rt and Rref shown in FIG. If is a voltage control type direct current source, and supplies a direct current for converting a resistance value change of each of the resistors Rt and Rref into a voltage.
The direct current source If converts the current flowing through (Rt + Rref) into the input voltage Vin. Input voltage Vin
Is given by Vin = (Rt + Rref) × If, and is input to the AC amplifier 1 and the DC differential amplifier 3 for signal processing. The current flowing through the reference thermosensitive resistor Rref is converted into the detection voltage Viv. This detection voltage Viv is
It is compared with the reference voltage Vref by the DC differential amplifier 4 and feedback-controlled so that Viv = Vref is always maintained. That is, in order to make the voltage Viv obtained from the reference thermal resistor Rref constant (= Vref),
A feedback loop is formed by the DC differential amplifier 4, the reference voltage Vref, the integrator 5, and the DC current source If,
The output current from the voltage control type direct current source If is controlled so that the detection voltage Viv becomes constant. Further, the reference voltage Vr for detecting only the information of the radiant heat
By connecting two stages of ef in series, the reference voltage of the DC differential amplifier 3 becomes 2 × Vref, which is compared with the input voltage Vin.

The operation of the circuit shown in FIG. 2 will be described below. In FIG. 2, the detection voltage Viv is Viv = Rr.
It is given by ef × If, but is fixed at Viv = Vref by the action of the feedback loop. Since the resistance value of the reference thermosensitive resistor Rref is determined by the ambient temperature, the control voltage V4 of the DC current source If for keeping the detection voltage Viv constant can be handled as the ambient temperature information. Further, in the DC differential amplifier 3, a voltage that is twice the reference voltage Vref and an input voltage Vin.
By performing differential amplification with the output voltage V2,
Only radiant heat information can be extracted. This is because when there is no radiant energy from the outside, Rt = Rref holds even if the ambient temperature changes, and V
in = (Rt + Rref) × If = 2 × Rref × If
= 2 × Viv = 2 × Vref holds, and V2 = Vin−
This is because (2 × Vref) = 0. Therefore,
Even if the ambient temperature changes, the output voltage V2 is constantly 0.
The output voltage V2 appears only when V is maintained and the resistance value of the resistor Rt changes due to radiant heat. In addition, if there is no radiant energy incident, the input voltage V
in and the detection voltage Viv are kept constant, so that a constant sensitivity is always maintained regardless of changes in ambient temperature. Further, since Rt = Rref is constantly established with respect to changes in the ambient temperature, the sensor always operates with the highest sensitivity regardless of the temperature.

Further, as the output voltage V1, as in the conventional example, the input voltage Vin is AC-amplified by the AC amplifier 1, so that the variation of the radiant energy can be detected. The above three output voltages V1, V2
By using V4, it is possible to independently detect the amount of change in the radiant energy incident on the infrared sensitive resistor Rt, the absolute value of the radiant energy, and the ambient temperature.

[0021]

The infrared detecting circuit according to the present invention has the effect that the sensitivity does not change due to the ambient temperature, and that the sensitivity can be constantly maintained at a constant level. There is an effect that the variation of the incident radiant energy, the absolute value of the radiant energy, and the ambient temperature can be detected independently.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of an invention according to claim 1.

FIG. 2 is a circuit diagram showing a configuration of an invention according to claim 2.

FIG. 3 is a circuit diagram showing a conventional infrared detection circuit.

FIG. 4 is a characteristic diagram showing a typical resistance value-temperature characteristic of an infrared sensitive resistor.

FIG. 5 is a diagram showing a schematic configuration of a human body movement detection device using an infrared detection circuit.

FIG. 6 is a waveform diagram showing an operation of a human body movement detection device using an infrared detection circuit.

FIG. 7 is a diagram showing a change in sensitivity of a conventional infrared detection circuit depending on ambient temperature.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 AC amplifier 2 DC amplifier 3 DC differential amplifier 4 DC differential amplifier 5 Integrator Is DC current source If Voltage-controlled DC current source Rt Infrared sensitive resistor Rref Reference thermosensitive resistor Vref Reference voltage Vin Input voltage

Claims (2)

[Claims] 1. An infrared sensitive resistor sensitive to infrared radiant energy and ambient temperature, a reference thermal sensitive resistor sensitive to a change in ambient temperature with substantially the same temperature-resistance characteristic as the infrared sensitive resistor, and the infrared ray. A direct current source for supplying a current to a series circuit of the sensitive resistor and the reference thermosensitive resistor, an AC amplifier for AC-amplifying the first voltage obtained in the series circuit, and a first thermosensitive resistor provided to the reference thermosensitive resistor. 2 voltage 2
An infrared detection circuit comprising: a DC amplifier that amplifies twice and a DC differential amplifier that amplifies a difference between the output voltage of the DC amplifier and the first voltage. 2. An infrared sensitive resistor sensitive to infrared radiant energy and ambient temperature, a reference thermal resistor sensitive to ambient temperature change with substantially the same temperature-resistance characteristic as the infrared sensitive resistor, and the infrared ray. A voltage-controlled DC current source for flowing a current through a series circuit of a sensitive resistor and the reference thermosensitive resistor, an AC amplifier for AC-amplifying the first voltage obtained in the series circuit, and the reference thermosensitive resistor A first DC differential amplifier for amplifying the difference between the second voltage and the reference voltage obtained in step 1, an integrator for integrating the output voltage of the first DC differential amplifier, and the second voltage for the reference voltage. A feedback circuit that feeds back the output voltage of the integrator as a control voltage of the voltage-controlled DC current source so as to be equal, and a second circuit that amplifies a difference between the voltage twice the reference voltage and the first voltage. With DC differential amplifier An infrared detection circuit characterized in that